Towards quantification of toxicity of lithium ion battery electrolytes - development and validation of a liquid-liquid extraction GC-MS method for the determination of organic carbonates in cell culture materials.

A novel method based on liquid-liquid extraction with subsequent gas chromatography separation and mass spectrometric detection (GC-MS) for the quantification of organic carbonates in cell culture materials is presented. Method parameters including the choice of extraction solvent, of extraction method and of extraction time were optimised and the method was validated. The setup allowed for determination within a linear range of more than two orders of magnitude. The limits of detection (LODs) were between 0.0002 and 0.002 mmol/L and the repeatability precisions were in the range of 1.5-12.9%. It could be shown that no matrix effects were present and recovery rates between 98 and 104% were achieved. The methodology was applied to cell culture models incubated with commercial lithium ion battery (LIB) electrolytes to gain more insight into the potential toxic effects of these compounds. The stability of the organic carbonates in cell culture medium after incubation was studied. In a porcine model of the blood-cerebrospinal fluid (CSF) barrier, it could be shown that a transfer of organic carbonates into the brain facing compartment took place. Graphical abstract Schematic setup for the investigation of toxicity of lithium ion battery electrolytes.

Fragrance material review on phenethyl formate.

A toxicologic and dermatologic review of phenethyl formate when used as a fragrance ingredient is presented. Phenethyl formate is a member of the fragrance structural group Aryl Alkyl Alcohol Simple Acid Esters (AAASAE). The AAASAE fragrance ingredients are prepared by reacting an aryl alkyl alcohol with a simple carboxylic acid (a chain of 1-4 carbons) to generate formate, acetate, propionate, butyrate, isobutyrate and carbonate esters. This review contains a detailed summary of all available toxicology and dermatology papers that are related to this individual fragrance ingredient and is not intended as a stand-alone document. Available data for phenethyl formate were evaluated, then summarized, and includes: physical properties, acute toxicity, skin irritation, skin sensitization, and genotoxicity data. A safety assessment of the entire AAASAE will be published simultaneously with this document. Please refer to Belsito et al. (2012) for an overall assessment of the safe use of this material and all AAASAE in fragrances.

Fragrance material review on 1,1-dimethyl-2-phenylethyl formate.

A toxicologic and dermatologic review of 1,1-dimethyl-2-phenylethyl formate when used as a fragrance ingredient is presented. 1,1-Dimethyl-2-phenylethyl formate is a member of the fragrance structural group Aryl Alkyl Alcohol Simple Acid Esters (AAASAE). The AAASAE fragrance ingredients are prepared by reacting an aryl alkyl alcohol with a simple carboxylic acid (a chain of 1-4 carbons) to generate formate, acetate, propionate, butyrate, isobutyrate and carbonate esters. This review contains a detailed summary of all available toxicology and dermatology papers that are related to this individual fragrance ingredient and is not intended as a stand-alone document. Available data for 1,1-dimethyl-2-phenylethyl formate were evaluated, then summarized, and includes: physical properties; acute toxicity; skin irritation; mucous membrane (eye) irritation; skin sensitization; and genotoxicity data. A safety assessment of the entire AAASAE will be published simultaneously with this document. Please refer to Belsito et al., 2012 for an overall assessment of the safe use of this material and all AAASAE in fragrances.

Fragrance material review on benzyl formate.

A toxicologic and dermatologic review of benzyl formate when used as a fragrance ingredient is presented. Benzyl formate is a member of the fragrance structural group Aryl Alkyl Alcohol Simple Acid Esters (AAASAE). The AAASAE fragrance ingredients are prepared by reacting an aryl alkyl alcohol with a simple carboxylic acid (a chain of 1-4 carbons) to generate formate, acetate, propionate, butyrate, isobutyrate and carbonate esters. This review contains a detailed summary of all available toxicology and dermatology papers that are related to this individual fragrance ingredient and is not intended as a stand-alone document. Available data for benzyl formate were evaluated, then summarized, and includes physical: properties, acute toxicity, skin irritation, mucous membrane (eye) irritation, skin sensitization, and genotoxicity data. A safety assessment of the entire AAASAE will be published simultaneously with this document. Please refer to Belsito et al., 2012 for an overall assessment of the safe use of this material and all AAASAE in fragrances.

Fragrance material review on anisyl formate.

A toxicologic and dermatologic review of anisyl formate when used as a fragrance ingredient is presented. Anisyl formate is a member of the fragrance structural group Aryl Alkyl Alcohol Simple Acid Esters (AAASAE). The AAASAE fragrance ingredients are prepared by reacting an aryl alkyl alcohol with a simple carboxylic acid (a chain of 1-4 carbons) to generate formate, acetate, propionate, butyrate, isobutyrate, and carbonate esters. This review contains a detailed summary of all available toxicology and dermatology papers that are related to this individual fragrance ingredient and is not intended as a stand-alone document. Available data for anisyl formate were evaluated, then summarized, and includes: physical properties, acute toxicity, skin irritation, and skin sensitization data. A safety assessment of the entire AAASAE will be published simultaneously with this document. Please refer to Belsito et al. (2012) for an overall assessment of the safe use of this material and all AAASAE in fragrances.

Characteristic effects of methylglyoxal and its degraded product formate on viability of human histiocytes: a possible detoxification pathway of methylglyoxal.

Methylglyoxal (MGO) is a toxic and highly reactive alpha-oxoaldehyde, elevated in the states of various diseases underlying enhanced oxidative stress. Furthermore, MGO has been reported to generate another aldehyde, formic acid (FA). In this sense, investigating the biological property of FA is crucially important. The present study examined the effects of MGO and FA on cell viability using the U937 human histiocytic cell line. FA showed a dose-dependent increase in cell viability at the concentrations of MGO in which cell viability decreased. The mechanism of the increase by FA involved the presence of endogenous hydrogen peroxide (H2O2) and tetrahydrofolate in the folate pathway, whereas that of the decrease in cell viability by MGO involved interaction with H2O2 and oxidative damage. These findings suggest that FA production by MGO degradation may play a role in attenuation of oxidative cellular injury caused by MGO. We hypothesize that FA generation pathway constitutes a detoxification system for MGO.

[Two cases of methanol poisoning with chronological measurements of blood concentrations of methanol, ethanol and formate].

We report two cases of methanol poisoning and evaluate the kinetics of methanol, ethanol, and formate. The first case was a 48-year-old man (case 1). His initial methanol level was 56.4 mg/dL and serum ethanol level was 2.4 mg/dL. Serum formate was not detected, and ethanol administration was initiated. However, methanol was eliminated slowly, and serum formate increased. His methanol and formate levels decreased rapidly following hemodialysis. He was discharged without any sequelae. The second case was a 35-year-old man (case 2). His serum methanol level was 400 mg/dL, and serum ethanol was not detected. His serum formate level was 13.4 mg/dL, and ethanol and activated folate were administered. He underwent hemodialysis immediately after diagnosis. Methanol and formate decreased rapidly, and he was discharged without any sequelae. Methanol and formate are eliminated slowly if ethanol is administered alone. We suggest that hemodialysis should be considered immediately after ethanol administration.

Species differences in methanol and formic acid pharmacokinetics in mice, rabbits and primates.

Methanol (MeOH) is metabolized primarily by alcohol dehydrogenase in humans, but by catalase in rodents, with species variations in the pharmacokinetics of its formic acid (FA) metabolite. The teratogenic potential of MeOH in humans is unknown, and its teratogenicity in rodents may not accurately reflect human developmental risk due to differential species metabolism, as for some other teratogens. To determine if human MeOH metabolism might be better reflected in rabbits than rodents, the plasma pharmacokinetics of MeOH and FA were compared in male CD-1 mice, New Zealand white rabbits and cynomolgus monkeys over time (24, 48 and 6h, respectively) following a single intraperitoneal injection of 0.5 or 2g/kg MeOH or its saline vehicle. Following the high dose, MeOH exhibited saturated elimination kinetics in all 3 species, with similar peak concentrations and a 2.5-fold higher clearance in mice than rabbits. FA accumulation within 6h in primates was 5-fold and 43-fold higher than in rabbits and mice respectively, with accumulation being 10-fold higher in rabbits than mice. Over 48 h, FA accumulation was nearly 5-fold higher in rabbits than mice. Low-dose MeOH in mice and rabbits resulted in similarly saturated MeOH elimination in both species, but with approximately 2-fold higher clearance rates in mice. FA accumulation was 3.8-fold higher in rabbits than mice. Rabbits more closely than mice reflected primates for in vivo MeOH metabolism, and particularly FA accumulation, suggesting that developmental studies in rabbits may be useful for assessing potential human teratological risk.

Formate pharmacokinetics during formate administration in folate-deficient young swine.

The objective of the study was to investigate the effect of folate deficiency on formate pharmacokinetics during formate administration in folate-deficient young swine. Methanol is a one of the congeners found in alcoholic beverages. Methanol toxicity is mediated through formic acid and thus plays a significant role in the pathophysiology of alcoholism. Folate is a required cofactor in the metabolism of formate to CO(2) and H(2)O. We investigate the effect of folate deficiency on the pharmacokinetics of formate. Twelve young pigs were pair-matched and randomly placed into 2 groups on acquisition ( approximately 5 weeks). One group was made folate deficient (FFD) by feeding with a folic acid-deficient diet; the other group (FFC) was fed a diet supplemented with folate. Four animals (31-38 kg) from each group were infused (intravenous) with 351 mg/kg of sodium formate. The remaining 2 animals were infused with isotonic sodium chloride solution. Blood samples were collected before and at 10, 20, 30, 45, 60, 90, 120, 180, 240, and 480 minutes post dose and analyzed for formate levels by gas chromatography. Pharmacokinetic parameters were estimated using a noncompartmental approach. Formate (mean +/- SE) accumulation was higher in the FFD group than the FFC group (AUC(0-infinity) of 72.37 +/- 8.29 vs 30.08 +/- 2.58 g min/L, respectively). Elimination was also slower in the FFD group (FFD systemic clearance = 0.12 +/- 0.01 L/min compared with FFC systemic clearance = 0.27 +/- 0.02 L/min). Half-life of elimination was 2.5 times longer in FFD group (113 +/- 1 minute) than in FFC group (45 +/- 6 minutes). Folate deficiency had no influence on the volume of distribution of formate (18.84 +/- 1.05 L in FFD vs 17.21 +/- 1.35 L in FFC). Adequate folate status is important in the elimination of formate. A folate-deficiency state results in a reduction in formate elimination kinetics, which may increase the risk of formate toxicity.

Preparation and biodistribution of 99mTc-tricarbonyl complex with 4-[(2-methoxyphenyl)piperazin-1-yl]-dithioformate as a potential 5-HT1A receptor imaging agent.

The goal of this study is to develop a novel 5-HT(1A) receptor imaging agent. 4-[(2-methoxyphenyl)piperazin-1-yl]-dithioformate (MPPDTF) was labeled with (99m)Tc-tricarbonyl core via dithioformate moiety in high yield (>96% by HPLC). (99m)Tc(CO)(3)-MPPDTF is a neutral and lipophilic complex, which was confirmed by paper electrophoresis and octanol/water partition coefficient (P=27.0+/-1.4, n=3), respectively. In vivo biodistribution indicated that this complex had moderate brain uptake (0.53+/-0.10% ID/g at 5 min and 0.42+/-0.02% ID/g at 120 min) and good retention (about 80% of the activity was retained in the brain at 120 min post-injection). Regional brain distribution study showed that hippocampus, where the 5-HT(1A) receptor density is high, had the highest uptake (0.60+/-0.02% ID/g at 5 min p.i.) and the cerebellum, where the 5-HT(1A) receptor density is low, had the lowest uptake (0.10+/-0.02% ID/g at 5 min p.i.). After blocking with 8-OH-DPAT, the hippocampus uptake was decreased obviously while the cerebellum uptake was increased slightly. This result indicates that (99m)Tc(CO)(3)-MPPDTF complex has specific binding to 5-HT(1A) receptor.

Methanol and formate kinetics during treatment with fomepizole.

OBJECTIVE: Methanol is metabolized by alcohol dehydrogenase to formaldehyde, and further to formic acid, which is responsible for the toxicity in methanol poisoning. Fomepizole (4-methylpyrazole) is a potent competitive inhibitor of alcohol dehydrogenase and is used as an antidote to treat methanol poisonings. We report serum methanol kinetics in eight patients treated with bicarbonate and fomepizole only. METHODS: Prospective case series study of eight patients with methanol poisoning, who were selected to fomepizole and bicarbonate treatment only, because of moderate metabolic acidosis. Three of the patients were later dialyzed, because of high serum methanol concentrations and very slow methanol elimination. RESULTS: Upon admission the median pH was 7.27 (range 7.12-7.50), median base deficit was 15 mmol/L (5-22 mmol/L) and median serum methanol was 20.4 mmol/L (65 mg/dL) (range 8.4-140.6 mmol/L). The kinetics of methanol during fomepizole treatment in six patients was best described by a first-order elimination one-compartment model. The mean correlation coefficient (R2) describing the first-order elimination model in all eight patients was 0.95 (range 0.90-0.99). The mean plasma half-life (t(1/2)) of methanol during fomepizole treatment was 52 h (range 22-87); the higher the serum methanol, the longer the T(1/2). Mean half-life of serum formate was 2.6 h, when methanol metabolism was assumed blocked by fomepizole and no folinic acid was given. This rapid formate elimination in nonacidotic patients may be explained by high renal excretion of formate. CONCLUSION: Based on our data, methanol-poisoned patients with moderate metabolic acidosis and methanol levels up to 19 mmol/L (60 mg/L) may safely be treated with bicarbonate and fomepizole only, without dialysis.

Formate kinetics in methanol poisoning.

OBJECTIVE: The objective is to describe the kinetics of formate, the main toxic metabolite of methanol, in a series of consecutive patients treated in the same intensive care unit for severe methanol poisoning. METHODS: The charts of the patients admitted between 1987 and 2001 were reviewed. Inclusion criteria were: a history of deliberate methanol ingestion, with a blood methanol concentration greater than 20 mg/dL (6.2 mmol/L) or a high anion gap metabolic acidosis. Indications for hemodialysis were: blood methanol concentration >50 mg/dL (15.8 mmol/L), metabolic acidosis (bicarbonate <15 mmol/L, arterial pH <7.30), visual toxicity. Antidotal therapy included ethanol administration in 22 cases, and fomepizole in three cases. Serial blood measurements were obtained for pH, bicarbonate, methanol and formate. Endogenous and hemodialysis elimination half-lives were calculated as t1/2 =0.693/Ke. Fick principle was applied for hemodialysis clearance calculation. RESULTS: The records of 25 methanol poisoned patients were analysed. Among them, 18 patients had sufficient data to allow accurate determinations of formate kinetics. Formate half-life elimination during hemodialysis was 1.80+/-0.78 h, which was statistically different from the values observed before or in the absence of dialysis (6.04+/-3.26 h, P =0.004). The mean hemodialysis formate clearance rate calculated in eight cases was 176+/-43 mL/min. A rebound in plasma formate concentration was observed in three patients after the discontinuation of hemodialysis. CONCLUSIONS: In accordance with previous isolated case reports and in contrast with a recent case series, our data document that hemodiaysis is effective in reducing formate elimination half-life. The impact on clinical outcome is still debatable.

Relative bioavailability of calcium from calcium formate, calcium citrate, and calcium carbonate.

Calcium is an essential nutrient required in substantial amounts, but many diets are deficient in calcium making supplementation necessary or desirable. The objective of this study was to compare the oral bioavailability of calcium from calcium formate, a new experimental dietary calcium supplement, to that of calcium citrate and calcium carbonate. In a four-way crossover study, either a placebo or 1200 mg of calcium as calcium carbonate, calcium citrate, or calcium formate were administered orally to 14 healthy adult female volunteers who had fasted overnight. After calcium carbonate, the maximum rise in serum calcium ( approximately 4%) and the fall in serum intact parathyroid hormone 1-84 (iPTH) (approximately 20-40%) did not differ significantly from placebo. After calcium citrate, the changes were modestly but significantly (p < 0.05) greater, but only at 135 to 270 min after ingestion. In contrast, within 60 min after calcium formate serum calcium rose by approximately 15% and serum iPTH fell by 70%. The mean increment in area under the plasma concentration-time curve (0-270 min) for serum calcium after calcium formate (378 mg . min/dl) was double that for calcium citrate (178 mg . min/dl; p < 0.01), whereas the latter was only modestly greater than either placebo (107; p < 0.05) or calcium carbonate (91; p < 0.05). In this study, calcium formate was clearly superior to both calcium carbonate and calcium citrate in ability to deliver calcium to the bloodstream after oral administration. Calcium formate may offer significant advantages as a dietary calcium supplement.

Metabolite comparisons and the identity of nutrients translocated from symbiotic algae to an animal host.

Dinoflagellate algae of the genus Symbiodinium in symbiosis with marine animals release much of their photosynthetic carbon to the animal host. The compounds translocated to the host ('mobile compounds') were investigated by metabolite comparison as follows: a substrate was identified as a candidate mobile compound when comparable profiles of metabolites were generated from host metabolism of this substrate (supplied exogenously) and the endogenous mobile compounds. When the sea anemone Anemonia viridis was incubated with NaH14CO2 under photosynthesizing conditions, most of the radioactivity in the animal tissue was recovered from the low-molecular-mass fraction and distributed in the ratio 1:2:1 between the neutral, acidic and basic sub-fractions. Prominent 14C-labelled compounds included glucose, malate and glucose-6-phosphate. When the symbiosis was incubated with 14C-labelled glucose plus succinate or fumarate (but none of eight other substrate combinations tested), the 14C-labelled metabolites closely matched those obtained with NaH14CO2. These data suggest that glucose and succinate/fumarate (or metabolically allied compounds) may be important photosynthetic compounds transferred from the Symbiodinium cells to the tissues of A. viridis. Metabolite comparisons can be applied to study nutritional interactions in symbioses involving photosynthetic algae and, with appropriate modification, other associations between microorganisms and plants or animals.

Fragrance material review on linalyl formate.

A toxicologic and dermatologic review of linalyl formate when used a a fragrance ingredient is presented.

Post-mortem analysis of formic acid disposition in acute methanol intoxication.

Fifteen cases of fatal massive methanol intoxication have been investigated. Victims received either no treatment or ethanol therapeutic treatment. Methanol poisoning cases were classified in three groups according to survival time: more than 3 days (group 1), up to 3 days (group 2) and few hours (group 3). Body distribution of methanol and formic acid, as the main metabolite, was analyzed in blood and in different organs (brain, kidney, lung and liver). Relationships between formic acid concentration in the different tissues, survival time and type of treatment applied to victims were studied. Formic acid in blood and tissues was analyzed by head space gas chromatography (head space-GC) with FID detector, previous transformation in methyl formate, essentially as described by Abolin. Formic acid concentration was between 0.03 and 1.10g/l in the samples under study. A good correlation between blood and brain, but poor between blood and the remaining tissues was found. Obtained data suggested that the use of blood and brain could help to improve the analysis of formic acid intoxication. The best correlation among organs was found between lung and kidney for all groups (r(2)=0.91, 0.84 and 0.87, corresponding to groups 1, 2 and 3, respectively). Lethality index was defined as LI = (concentration of formic acid in blood in (g/l)/0.5) x 100, taking into account that 0.5g/l is the concentration reported by Mahieu in severe methanol poisoning. LI parameter was used to estimate formic acid incidence on the lethality of methanol poisoning cases. LI showed a good correlation with total formic acid concentration of the different tissues analyzed (r(2)=0.80). Furthermore, LI allowed us to discriminate between individuals that received therapeutic treatment and survived different periods. LI>100 indicated a severe intoxication and short survival time if the victim was assisted with ethanol therapy and hemodialysis was not applied. With regard to victims who received no therapeutic treatment and died in few hours, LI was in the range 40-100. LI was below 40 for individuals that survived more than 3 days and hemodialysis was not performed. Results showed the importance of performing formic acid analysis to diagnose severe methanol intoxication in post-mortem cases.

Formate-stimulated NaCl absorption in the proximal tubule is independent of the pendrin protein.

A significant fraction of active chloride reabsorption across the apical membrane of the proximal tubule is mediated by a chloride/formate exchange process, whereby intracellular formate drives the transport of chloride into the cell. When chloride/formate exchange operates in parallel with Na(+)/H(+) exchange and H(+)-coupled recycling of formate, the net result is electroneutral NaCl reabsorption. Pendrin is the protein product of the PDS gene (SLC26A4) and functions in several different anion exchange modes, including chloride/formate exchange. Pendrin is expressed in the kidney and may serve as the transporter responsible for formate-dependent NaCl reabsorption. In the present study, Pds-knockout mice were used to determine the role of pendrin in proximal tubule chloride reabsorption. We show that formate-dependent NaCl absorption in microperfused proximal tubules is similar between wild-type and pendrin-deficient mice. In addition, there is no difference in the rate of formate-mediated chloride transport in brush-border membrane vesicles isolated from wild-type and pendrin-deficient mice. These studies demonstrate that pendrin is not responsible for formate-dependent NaCl reabsorption in the proximal tubule.

Formate kinetics in methanol poisoning.

OBJECTIVE: We sought to describe the kinetics, dialysis clearance, and laboratory markers of formate (FA), the toxic metabolite of methanol (meOH). METHODS: Data were obtained from a prospective, multicenter study of fomepizole +/- dialysis for methanol poisoning. Inclusion criteria confirmed methanol exposure or suspicion of exposure plus either acidemia or abnormal osmolar gap. Dialysis indications were [meOH] > 50 mg/dL, pH < 7.1, refractory acidosis, or visual toxicity. Serial plasma formate, methanol, pH, and electrolyte measurements were made. Formate was determined by gas chromatography. Endogenous and dialysis elimination half-lives were calculated as t(1/2) = 0.693/Ke, with Ke (elimination constant) derived from the slope of log (FA) vs. time. Half-lives were compared with an unpaired Student's t-test. Dialysis clearance was calculated using the Fick Principle. Pearson correlation analysis compared initial formate with initial pH, serum bicarbonate, and anion gap. RESULTS: Eleven patients were treated in the study. Eight had detectable formate with mean [FA] of 15.1 mmol/L (range 0.5-34.8). Endogenous elimination half-life was 205 +/- 90 minutes. Elimination half-life during dialysis (n = 5) was 150 +/- 37 minutes, which was not different (t = 0.22; NS). The overall dialysis formate clearance rate was 223 +/- 25 mL/min. Correlation coefficients were: pH vs. formate r2 = 0.93; bicarbonate vs. formate r2 = 0.81; and anion gap vs. formate r2 = 0.76 (all p < 0.05). CONCLUSIONS: Although dialysis clears formate, it did not significantly enhance endogenous elimination in our series of patients. Low pH, low bicarbonate, and elevated anion gap correlate independently with formate presence.

Human pendrin expressed in Xenopus laevis oocytes mediates chloride/formate exchange.

Pendred syndrome, characterized by congenital sensorineural hearing loss and goiter, is one of the most common forms of syndromic deafness. The gene causing Pendred syndrome (PDS) encodes a protein designated pendrin, which is expressed in the thyroid, kidney, and fetal cochlea. Pendrin functions as an iodide and chloride transporter, but its role in the development of hearing loss and goiter is unknown. In this study, we examined the mechanism of pendrin-mediated anion transport in Xenopus laevis oocytes. Unlabeled formate added to the uptake medium inhibited pendrin-mediated (36)Cl uptake in X. laevis oocytes. In addition, the uptake of [(14)C]formate was stimulated in oocytes injected with PDS cRNA compared with water-injected controls. These results indicate that formate is a substrate for pendrin. Furthermore, chloride stimulated the efflux of [(14)C]formate and formate stimulated the efflux of (36)Cl in oocytes expressing pendrin, results consistent with pendrin-mediated chloride/formate exchange. These data demonstrate that pendrin is functionally similar to the renal chloride/formate exchanger, which serves as an important mechanism of chloride transport in the proximal tubule. A similar process could participate in the development of ion gradients within the inner ear.

Membrane permeability of formate in human erythrocytes: NMR measurements.

The rate of the rapid exchange of formate mediated by band 3 in human erythrocytes, under equilibrium exchange conditions, was measured by using a T1 relaxation method with 13C-labelled formate and 13C NMR, and a pulsed field-gradient spin-echo (PFGSE) method using 1H NMR. The former analysis was based on large differences in T1 between the inside and the outside of the cells brought about by added Mn2+; the latter was based on large differences in the apparent diffusion coefficient inside and outside the cells. There was close agreement in the estimates of the membrane permeabilities made using both methods, suggesting a lack of interference of the exchange process by Mn2+. Regression analysis yielded estimates (under the specified conditions, including 37 degrees C) of Vmax of 3.5 +/- 0.3 x 10(-9) and 3.8 +/- 0.4 x 10(-9) mol cm-2 s-1, and K(m) of 9.8 +/- 0.2 and 8.1 +/- 0.2 mM, for the T1 and the PFGSE methods, respectively. These are new estimates made using methodology that has not previously been applied to measuring rapid (sub-second time scale) formate exchange in cells.